Actually getting back on topic for a sec - someone above mentioned that their 60mpg car in 5 years would put out less CO2 than a 30year old landrover.
This is technically correct, but if you have to make a new car every 5 years this is incredibly costly in terms of CO2 and dangerous emmission's. Whatcar have just done a green-car survey, and it points out that the new landrover discovery is greener to manufacture than a toyota prius. If the LR lasts you 20 years and the prius only 10, you're still better off keeping the LR going as long as it can. Since these new hybric cars are incredibly complex there is more manafacturing required - hence less green.
Painting a car is perhaps the worst environmentally damaging thing you can do - the amount of noxious chemical's that are used are incredible.
I'm surprised that FOTE or Greenpeace has not done research on this. e.g. if you keep an old car going for 10 years instead of buying a newer model, you save X amount of co2, chemicals, etc.etc.
The short of it is if you buy a car keep it going as long as you can, if you want to me more green!